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. 2025 Jul 4;12(10):nwaf268. doi: 10.1093/nsr/nwaf268

Figure 4.

Figure 4.

Magnetic and stress measurement of the La3Ni2O7–δ sample at 20 GPa. (a) Fluorescence image of sample C (La3Ni2O7–δ in silicon oil). The edge of the sample is outlined by the black dashed line. (b) ODMR splitting of the NV centers during the ZFC-FW and FC processes, with an external magnetic field of around 120 G. The NV positions are marked in (a). Both the diamagnetism of the La3Ni2O7–δ sample and the local stress contribute to the ODMR splitting. (c, d) Stress distribution revealed by the zero-field ODMR spectra at 150 K (>Tc). The center frequency of the ODMR spectra (c) reveals the compressive stress, while the splitting of the ODMR spectra (d) is proportional to the differential stress. (e) Magnetic image under an external magnetic field of around 120 G after ZFC. Note that the contribution of the stress distribution has been subtracted by the results shown in (c and d). The region on the gray square is an odd point and is therefore not included in the discussion. (f) Comparison of the diamagnetism effect of the three samples during ZFW-FW measurement. The external magnetic field is around 120 G. For each point, the ODMR splitting at high temperatures (>Tc) is used as the reference to calculate ΔBZ.